Whether Euchoreutes is actually a member of either of the two dipodid clades that have been recognised in phylogenetic studies of this group - Dipodinae and Allactaginae (Shenbrot 1992) - remains uncertain.

Now Dr Michael Lee of the South Australian Museum in Adelaide, Australia, has repeated the exercise using the same technique, known as phylogenetic analysis, only this time applying a more sophisticated statistical method.

Gibbs said that might have been a coincidence, but the unusual placement of the virus on what what virologists call phylogenetic trees-a sort of schematic family history of the virus -- also peeked his interest.

Using a method of comparing genetic characteristics, called phylogenetic analysis, the researchers studied a group of men who had sexually transmitted their HIV viruses; in this way the team was able to determine the source of rapidly mutating HIV viruses by analyzing the viral sequences extracted from the blood and semen of HIV transmitting partners.